Direct positive silver halide emulsion containing a dye with at least one naptho (2 3 ) oxazole nucleus

ABSTRACT

A fogged direct positive silver halide photographic emulsion containing a dye selected from the group represented by the following formulae:   D R A W I N G

United States Patent [72] lnventors Kelaulre Shlba;

Masanao Hinata; Aklra Sato; Masao Sawahara, all 0! Kanagawa, Japan [2]] Appl. No. 1,488

[22] Filed Jan. 8, 1970 [45] Patented Oct. 26, 1971 [73] Assignee Fuji Photo Flint Co., Ltd.

Kanagawa, Japan [32] Priority Jan. 8, 1969 [33] Japan [54] DIREIZT POSITIVE SILVER IIALIDE EMULSION CONTAINING A DYE WITH AT LEAST ONE NAPIHO (2,31!) OXAZOLE NUCLEUS Primary Examiner- Norman G. Torchin Assistant Examiner Richard E. Fichter Attorney-Sughrue, Rothwell, Mion, Zinn & Macpealt ABSTRACT: A fogged direct positive silver halide photographic emulsion containing a dye selected from the group represented by the following formulae:

wherein R and R which may be the same or different, each represents an alkyl group, an alkoxyalkyl group. a hydroxyalkyl group, a carboxyalkyl group, a sulphoalkyl group. an ally] group, an aralkyl group. or a substituted aralkyl group, L is a methine chain or a methine chain substituted by alkyl or aryl groups; 2 is an atomic group necessary to complete a 5- or 6-membered nitrogen containing heterocyclic nucleus; Q is an atomic group necessary to complete a 5- or 6- membered heterocyclic nucleus; m and p are individually (l. lor2; Xis ananionandn isOor I.

PATENTED'UBT 2 8 IBYI 3, 6 1 5 64 3 DENSITY LOG.E

DENSITY LOG.E

INVENTORS KEISUKE SHIBA MASANAO mum AKIRA SATO MASAO SAWAHARA S Kr 'K-M, M I

2;... & M

ATTORNEYS DIRECT POSITIVE SILVER IIALIDE EMULSION CONTAINING A DYE WITH AT LEAST ONE NAPTHO (23d) OXAZOLE NUCLEUS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a silver halide photographic emulsion and, more particularly, a fogged direct positive photo graphic emulsion.

Description of the Prior Art It is well known to add a sensitizing dye to a fogged silver halide photographic emulsion capable of directly giving a positive image through exposure and development in order to spectrally sensitize the silver halide photographic emulsion and to raise the overall sensitivity. During the same time, as is known, the contrast changes with the variety and amount of the sensitizing dye added although the overall sensitivity of the silver halide photographic emulsion is raised.

Generally, the overall sensitivity of a direct positive photographic emulsion is markedly raised by increasing the amount of sensitizing dye added thereto but, in many cases, the maximum density (D/max) and contrast are thereby decreased, often resulting in insufficient images.

Furthermore, in some cases, when sensitizing a direct positive photographic emulsion by adding a sensitizing dye thereto, the overall sensitivity is raised but re-reversal" is too large to give sufficient whiteness. Rereversal means that the density increases after decreasing in the characteristic curve, as shown by the dotted portion of curve 1 in FIG. I.

This re-reversal" depends on the method of preparation of a silver halide emulsion and more remarkably on the variety of sensitizing dye added. Accordingly, a sensitizing dye causing a large "re-reversal cannot be put to practical use as it is.

It is the principal object of the present invention to provide a high sensitivity. direct positive silver halide photographic emulsion possessing a low minimum density without "rereversal," while holding a predetermined maximum density as well as high contrast.

SUMMARY OF THE INVENTION The above-mentioned object can be accomplished by incorporating in a direct positive silver halide photographic emulsion a cyanine dye or a merocyanine dye represented by the following general formulas I and II, respectively:

benzoxazoles, naphthoxazoles, thiazolines, thiazoles, benzothiazoles, naphthothiazoles, selenazoles, benzoselenazoles, naphthoselenazoles, quinolines and pyridines, Q is an atomic group necessary to complete a fivemembered or six-membered heterocyclic nucleus, for example, rhodanines, oxazolido-S-on-Z-thiones, thiohydantoins, pyrazole-S-ones and tltiobarbituric acids, m and p are 0, l or 2.1: is an anion and n isO or 1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I represents the characteristic curve of a photographic emulsion undergoing the re-reversal" phenomenon.

FIG. 2 represents the characteristic curves of photographic material containing no sensitizing dye, a conventional dye and the sensitizing dye of the present invention, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the sensitizing dyes represented by the general formulas (I) or (II) are given below, and are merely illustrative, and not limiting, in nature.

Comparison Dye B Comparison Dye F Hi jlHu Cl a Dye 13 55 Comparison Dye G Comparison Dye A 70 on,

0 0 Comparison Dye I l C-CH=CHCH=C i g]/ \N I 75 g CCH=CHCH=C Q I CzHu C1115 N I CH; CH:

Comparison Dye K It has already been disclosed in Japanese Patent publication No. 4l25/l968, US. Pat. No. 2,323,187 and French Patent No. l,520,822 that sensitizing cyanine dyes and merocyanine dyes are suitable for use to raise the spectral sensitivity of a direct positive silver halide photographic emulsion.

In the case of the spectral sensitization of a direct positive photographic emulsion with a sensitizing dye, however, the photographic characteristics of reversal, that is, spectral sensitivity, contrast, minimum density and re-reversal, differ with the variety of sensitizing dyes. This is unlike the spectral sensitization of the ordinary nonfogged emulsion. It is found that these photographic characteristics differ remarkably depend ing on the difference of structure, i.e., heterocyclic ring, or a sensitizing dye.

in the case where an ordinary sensitizing cyanine dye or merocyanine dye is incorporated into a direct positive silver halide photographic emulsion, there is a tendency for an increase of spectral sensitivity to be accompanied by a lowering of contrast, an increase of minimum density and an increase of "re-reversal.

As will be apparent from the examples described below, a direct positive silver halide photographic emulsion sensitized with a dye having at least one naphtho (2,3d) oxazole nucleus represented by the general formula (I) or (ll) has more excellent characteristics, such as higher sensitivity, less re-reversal and lower minimum density than an emulsion sensitized with a dye having no naphtho (2,3 d) oxazole nucleus, for example, benzoxazole, benzothiazole, naphtho (2,1 d) oxazole or naphtho (l,2) oxazole nucleus. A high-sensitive direct positive silver halide photographic emulsion can be obtained by incorporating a sensitizing dye represented by the general formula (l) or (II) into a direct positive silver halide photographic emulsion. The thus-sensitized emulsion is particularly suitable for use in the copying of documents.

Ordinarily it is preferable to add a dye of the general formula (l) or (ll) to an emulsion in the form ofa solution in a suitable solvent such as water, methanol or ethanol.

The amount of the dye to be added to a direct positive silver halide emulsion is substantially the same as in ordinary silver halide nonfogged emulsions, i.e., 0.5$0 mg. per kg. of the emulsion. One or more of the dyes may be used.

Silver salts such as silver chloride, silver bromide, silver chlorobromide, silver chloroiodide, silver iodobromide and silver chloroiodobromide may be used as the emulsion in the present invention.

The emulsifying and physical ripening of the silver halide emulsion used in the present invention are carried out in a manner similar to that employed for ordinary emulsions but, before emulsifying or during the physical ripening, a salt of a Group VIII metal, such as iridium or rhodium, may be added thereto. The silver halide emulsion used in the present invention is fogged to its maximum density by light or by adding a chemical fogging agent thereto. Such a chemical fogging agent must fog the silver halide without attacking it. Ordinarily, thiourea dioxide, stannous chloride, formaldehyde, or hydrazine may be used. After the fogging, the pH and pAg are controlled, as the occasion demands, and a solution of the dye of the present invention is then added to the emulsion with sufficient agitation and thencoated onto a support. Ordinary additives such as coating aids and hardeners may be added to the emulsion.

The following may be employed as the support: glass, a cellulose derivative film, a synthetic resin film or baryta paper.

The following examples further illustrate the present invention and are not intended to limit the same in any manner.

EXAMPLE I A silver chloroiodobromide emulsion (iodine l.3 mol percent, bromine 2.4 mol percent) was fogged with hydrazine dihydrochloride and the pH and pAg were respectively adjusted to 5.6 and 6.7. A predetermined amount of a dye solution having a concentration of l l0 mol/l was added to the emulsion, stirred adequately, applied to a cellulose triacctate base and dried. The resulting silver halide direct positive photographic light-sensitive material was exposed through a step wedge by means of a sensitometer. The light-sensitivc material was then developed with the following developer:

DEVELOPER metol --4 g.

hydroquinone l0 g.

anhydrous sodium sulfite t50 g.

anhydrous sodium carbonate 2.5 g.

mater to make I l.

The developed material was fixed with an ordinary sodium thiosulfate-containing fixing solution, washed with water and dried. Measurement of the optical density was carried out by means of a densitometer. The results are shown in table 1.

The sensitivity is represented by a relative value of the reciprocal of the amount of exposure required for giving a density of from one to times the sensitivity of an emulsion to which no sensitizing dye is added.

TABLE 1 Addition amount of dye solution per 1(1) g. of Minimum Sample No. Dye emulsion (mL) Sensitivity density 100 0. (l5 2 2-10 0. Oil 2 675 0. 07 4 1, 0. ll) 4 1, 6. 0. 09 4 2, 760 0.06

EXAMPLE ll A procedure similar to that described in example I was repeated except that a silver chloroiodide (iodine 1.3 mol percent) was used in place of the silver chloroiodobromide. The results are shown in table 2.

TABLE 2 Addition amount of dye solution per 'Iest 1(1) g. of Minimu No. Dye emulsion (1rd.) Sensitivity density a.- Nona. 100 0. 05 b Dye 4.. 1 2,770 0.05 c- B (eomparison) 1 283 0. m! d C (comparison)-.. 1 250 0. 11 8.-. Dyefi 1 2,llll 0.66 f D (comparison)... 1 437 0. t1 Dye 6 1 3, 640 0. 06 E (eomparison) 1 216 0.07 Dye 3 4 1,590 0.07 A (comparison)..- 4 250 n. is

it is evident from table 2 that the dyes having a naphtho (2,3 d) oxazole nucleus produce higher sensitivities and smaller minimum densities than the dyes having a naphtho (2,] d) oxazole nucleus or a naphtho (1,2 d) oxazole nucleus.

EXAMPLE III A silver chloroiodobromide emulsion (iodine 1.0 mol. percent, bromine 30 mol percent) was fogged with hydrazine 3. The fogged direct positive silver halide photographic emulsion as in claim 2, wherein said nitrogen-containing heterocyclic nucleus is selected from the group consisting of I oxazolines, oxazoles, benzoxazoles, naphthoxazoles, 'fhhydrochlonde and the PH and PAg were respecnvely thiazolines, thiazoles, benzothiazoles, nuphthothiazoles, J q P and A predetermmfid amount ofa 50mm) of selenazoles, benzoselenazoles, napthoselenazoles, quinolines sensmzmg y f afoncemratlon of 1X10l3 mol/1 was and pyridines, and wherein said heterocyclic nucleus is added to the emulsion, finned adequately and pp to 3 selected from the group consisting of rhodanines, oxazolido-S- lulose triacetate base. After drying, the resulting photographic n.2 thi lhiohydantoings .5 d hi b material was exposed through a step wedge by means of a senbim ig a id sitometer. The material after exposure wasdeveloped at 4. A photographic element comprising a support having C. for 2 minutes with the following developer. The developer thereon at least one layer of the fogged direct positive silver was used within 6 hours after preparation. halide emulsion of claim I.

5. A fogged direct positive silver halide photographic emul- D d 5 sion containing from 0.5 to 50 mg. per kg. of emulsion of a I dye selected from the group consisting of compounds anhydmus md'um summ represented by the following formulas: paral'ormaldehyde 7.5 g. potassium metahisulfite -2.6 g. g :onc nerd 7.. g. 2 0 U" ydroqumone --22.5 g. 3 potassium bromide l .6 g. water to make l l. Mull" N The results are shown in table 3, in which tests a to] cmi- A! ploy emulsions obtained from the same batch, and tests 9 toj 25 N employ emulsions obtained from another batch. HimSOr TABLE 3 Addition amount of dye solution per 100 Minimum Test No. Dye g. of em'u(lsitln)i Sensitivity Gamma density n 100 4. 2 0.05 b' Dye 3" 1 1, 010 4. 1 0.06 c- G (comparison). 1 3% 3. 2 0. 17 d H (comparison)... 1 2 2. 8 D. 18 o I (eomparis0n) 1 366 3.2 0.17 i K (eomparison) 1 196 2.3 0. 26 g None 100 4. 1 0. 04 ll'.- Dye 8 2 2,8) 4. 1 0. 04 i' J (comparison). 2 1,520 3.5 0.06 j F (comparison)... 2 892 3. 8 0.08

In FIG. 2, curves 2, 3 and 4 are the characteristic curves of CH; CH; a.,c and b in table 3, respectively. 0 What is claimed is: l. A fogged direct positive silver halide photographic emul C sion containing at least one cyanine for merocyanine-sensitizing dye, said dye having at least one naptho (2,3 d) oxazole nucleus. I &

2. The fogged direct positive silver halide photographic 2 2H5 emulsion as in claim 1, where said dye is selected from the o 0 group represented by the following formulas \I o C-OH=CHOH=C I c-L =L-L ...=o f f \N-' 03H; 01115 N it I 1 O 0 R (x).. and /c-on=c 11-0 H=C\ s x Q N i inci or (0110180311 0 N (I; O CH O\ 3 it I COH=CCH=C wherein R and R,, which may be the same or different, each ,t/

represents an alkyl group, an alkoxyalky] group, a hydroxyalf f kyl group, a carboxyalkyl group, a sulphoalkyl group, an allyl (CHmBOr (CH,);S0=H

group, an aralkyl group, or a substituted aralkyl group; L is a methine chain or a methine chain substituted by alkyl or aryl groups; Z is an atomic group necessary to complete a fiveor six-membered nitrogen containing heterocyclic nucleus; Q is an atomic group necessary to complete a fiveor six-mem- .bered heterocyclic nucleus; m and p are individually 0, l or 2;

X is an anion and n isO or I. 

2. The fogged direct positive silver halide photographic emulsion as in claim 1, where said dye is selected from the group represented by the following formulas:
 3. The fogged direct positive silver halide photographic emulsion as in claim 2, wherein said nitrogen-containing heterocyclic nucleus is selected from the group consisting of oxazolines, oxazoles, benzoxazoles, naphthoxazoles, thiazolines, thiazoles, benzothiazoles, naphthothiazoles, selenazoles, benzoselenazoles, naphthoselenazoles, quinolines and pyridines, and wherein said heterocyclic nucleus is selected from the group consisting of rhodanines, oxazolido-5-on-2-thiones, thiohydantoines, pyrazole-5-ons and thiobarbituric acids.
 4. A photographic element comprising a support having thereon at least one layer of the fogged direct positive silver halide emulsion of claim
 1. 5. A fogged direct positive silver halide photographic emulsion containing from 0.5 to 50 mg., per kg. of emulsion, of a dye selected from the group consisting of compounds represented by the following formulas: 